Engine Performance problem
1968 Mercury Monterey V8 Two Wheel Drive Automatic 120000 miles

I have a 1968 mercury monterey with a 390. i recently put a edelbrock performer rpm intake and edelbrock 750cfm carb on. I set the timing and put in a new set of points. without the vacuum advance on it runs fine from idle to mid rpm range. with the advance hooked up it chugs along just above idle making cruising and normal acceleration a pain.. once i get to high mid/ high rpms it smooths out and runs like a champ again.. i've tried adjusting the timing with the vacuum line on to see if it was getting to much or too little vacuum right away but it gets mildly to horribly better/worse... i'm ready to pull my hair out on this one. please help